The present invention relates to decoding fields. More particularly, it relates to a circuit for processing caption and picture data for synchronous display, in a decoder for decoding a transport stream, and a method of performing such data processing.
This application for a caption data processing circuit and method is based on Korean Patent Application No. 97-25221, which is incorporated herein by reference for all purposes.
Digital video technology can be applied to computer and home appliances as well as communication fields such as video conferencing and video telephones. Particularly, according to the MPEG-2 standard (which is to be adopted as a compression algorithm for digital satellite broadcasting systems, digital cable television and high-definition television) digital information is constituted of elementary streams each for video, audio, and data bit streams, and each of the elementary streams are packetized into a packetized elementary stream (PES) to be transmitted as a transport stream (TS).
Caption data is included in a video elementary stream to then be encoded and transmitted. Thus, a conventional caption data processing circuit, of a decoder for decoding a transport stream, extracts the PES from the transport stream, extracts a video elementary stream from the PES, and separates caption data from the video elementary stream to decode the separated caption data, thus outputting caption image data. Then, the caption image data is combined with picture data, to be displayed on a display.
However, since the conventional caption data processing circuit simply decodes only caption data without using a presentation time stamp (PTS), it is difficult to synchronize the decoded caption image data with the picture data, when the decoding time of the caption data is different from the time at which it should appropriately be presented.